Evolution; reproduction by splitting the body (Introduction)

by David Turell , Tuesday, May 21, 2024, 15:31 (184 days ago) @ David Turell

A fossil starfish in the act:

https://phys.org/news/2024-05-fossil-captures-starfish-million-years.html

"One of the wildest wonders of nature is the ability of some animals to reproduce by splitting in half. There is still so much we don't know about this process. So the discovery of a 155-million-year-old starfish fossil frozen partway through this process, published in a new study, could give scientists incredible new insights.

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"The starfish, or asteroid, is part of a group of animals called the echinoderms or spiny skinned animals that also includes sea lilies, sea urchins and sea cucumbers. They are found in almost every corner of our oceans and spend part of their life as microscopic larvae before developing into adults.

"Starfish are among the oldest living animals on our planet. They appeared in a form we would recognize almost 480 million years ago and have survived five mass extinctions.

"The reason for their evolutionary success could be in their ability to reproduce both sexually and asexually—by literally splitting in two and growing into two new animals. This is known as fissiparity. It is still sometimes observed in modern starfish and comes with the advantage of forming numerous offspring in a relatively short time and without "costing" the parent a great amount of energy or time.

"Sexual reproduction, on the other hand, requires starfish and brittle stars to come together in huge numbers to spawn. The disadvantage of fissiparity is that this type of reproduction can result in a lack of genetic diversity in the population.

"Biologists call the process of splitting in two parts fragmentation. Only a small number of animals can do this. For example, the common garden earthworm, which many gardeners have watched in amazement as one animal suddenly becomes two. Biologists can also watch starfish and brittle stars doing this in their labs or in marine stations.

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"Only a few animals make it into the fossil record, and many of these are in fragments as they often fall apart once the body has decayed. However, Thuy's brittle star discovery appears to show a brittle star in the process of reproducing asexually. The fossil has already been "born." One half of the body appears to be fully developed while the other half shows signs of regeneration with three smaller arms clearly visible."

Comment: Amoeba split in two, so the mechanism existed from the beginning. Sexual activity is highly complex and was an activity that had to be evolved over time. It is not surprising for this is to occur before sex appeared. Earth worms are still doing it from fragments if cut up. From the design viewpoint, the timing makes sense.